Liquefied m-phenylenediamine compositions for curing epoxy ether resins



2,893,973 Patented July 7, 1959 fire No Drawing. Application December 10, 1954 Serial No. 474,609

18 Claims. (Cl. 260-47) This invention relates to polyglycidyl ethers of polyhydric alcohols, commonly referred to as epoxy ether resins, and particularly to an improved composition for curing said resins.

It is known that epoxy ether resins are useful in the manufacture of varnishes, enamels, molding compositions, adhesives, films, fibers, molded articles, and the like. In order to cure or harden such epoxy ether resins and compositions containing them, various types of curing agents have been proposed, such as alkalies, sodium or potassium hydroxide, alkaliphenoxides like sodium phenoxides; carboxylic acids or anhydrides such as formic acid, oxalic acid or phthalic anhydride; Friedel-Crafts metal halides like aluminum chloride, zinc chloride, ferric chloride or boron trifluoride as well as complexes thereof with ethers, acid anhydrides, ketones, diazonium salts, etc.; phosphoric acid and partial esters thereof including n-butyl orthophosphate, diethyl orthophosphate and hexaethyl tetraphosphate; and amino compounds such as triethyl amine, ethylene diamine, diethyl amine, diethylene triamine, triethylene tetramine, pyridine, piperidine, dicyandiamide, m-phenylenediamine, melamine and the like. These substances are added and mixed with the epoxy resin or composition containing it in order to effect the curing or hardening thereof, the amounts varying considerably depending upon the particular agent or mixture of agents employed.

From among the foregoing hardening agents, the aromatic amines, especially m-phenylenediamine, are em.- ployed as the hardener for the epoxy resin because of the distinct advantage of producing a cured resin or composition of high heat distortion resistance. m-Phenylenediamine in substantially pure form, however, suffers the disadvantage of being a relatively high melting material, melting at approximately 60 -63 C. When used in commercial practice, it is necessary to melt the m-phenylenediamine and mix it with the epoxy resin to be hardened. The mixture will react at room temperature to form a hard resin representing a B stage resin. Under the influence of heat which may range anywhere from three to four hours at about 150 C. a complete cure of the epoxy resin is achieved. Since m-phenylenediamine is a solid and difficult to incorporate into the epoxy resin, whether the resin be a liquid at room temperature or liquefied by the application of heat, it is still necessary to blend the m-phenylenediamine with the resin at the melting point of the m-phenylenediamine which in the commercial grade may range anywhere from 70 to 80 C. This operation is very hazardous and in many' instances a highly exothermic reaction has been set oft under this condition. The high temperature required to melt the rn-phenylenediamine results in a relatively high temperature of the potting liquid thereby shortening the pot life of the resin.

In view of the foregoing shortcoming, attempts have been made to employ liquid amines as curing agents which would produce a material of high heat distortion resistance but without success.

It is an object of the present invention to provide a liquid catalyst adaptable for the initial or B stage curing of epoxy ether resins at room temperature followed by complete cure at elevated temperatures.

Other objects and advantages will become apparent 5 from the following specification.

, N-propyl acetamide We have found that blends of m-phenylenediamine containing from 10 to 50 percent by weight of a compound or a mixture of compounds selected from the class having the following formulae:

H: C O H:

Hg C\ 0 A and R1 R C O N/ wherein A represents either oxygen, =NI-I,

=NCH=CH or an :N-alkyl group, e.g., N-methyl, N-ethyl, N-propyl, N-butyl, etc., R represents either hydrogen or an alkyl group, e.g. methyl, ethyl, propyl, butyl, octyl, etc., R represents either hydrogen, allyl, or an alkyl group, e.g., methyl, ethyl, propyl, or butyl groups, and R represents an alkyl group of the same value as R are liquid at ordinary room temperatures, i.e. above 30 F. and exceptionally adaptable as liquid catalysts for blending with liquid epoxy ether resins.

The liquid catalysts react to the B stage at room. temperature and cure the resin at elevated temperatures to the same degree of hardness as that obtained by the use of commercial mphenylenediamine. The high temperature distortion point of the cured castings, as determined by the ASTM 648-45T method, is approximately the same as that obtained with m-phenylenediamine. The electrical properties are identical and exceptionally good.

The liquid catalysts prepared in accordance with the present invention are different from the existing liquid amines, etc., in that they will advance liquid epoxy resins rapidly to a B stage, which is stable for several months. All other presently known liquid amine type catalysts cause exothermic reactions and advance to an infusible stage, unless no reaction is initiated at all.

As illustrative specific compounds which may be used as such or in admixture, and hereinafter referred to for sake of expediency as liquefiers, characterized by the foregoing general formulae, the following may be mentioned:

Z-pyrrolidone N-methyl-Z-pyrrolidone N-ethyl-Z-pyrrolidone N-isopropyl-Z-pyrrolidone N-vinyl-Z-pyrrolidone Butyrolactone N-allyl formamide N-methyl fiormamide N-ethyl formamide N-propyl formamide N-butyl formamide N,N-dimethyl formamide N,N-diethyl formamide N,N-dipropyl formamide N,N-diisopropy1 formarnide N-allyl acetamide N-methyl acetamide N-ethyl acetamide N,N-diethyl acetamide N,N-dipropyl acetamide N-allyl propionarnide N-methyl propionamide N-ethyl propionamide N-propyl propionamide N,N-dimethyl propionarnide N,N-diethyl propionamide N,N-dipropyl propionamide N-allyl butyramide N-methyl butyramide N-ethyl butyramide N-propyl butyramide N,N-dimethyl butyramide N,N-diethyl butyramide N,N-dipropyl butyrami-de 'N-allyl tert. butyramide N-o ctyl caprylamide N-octyl capramide -N-butyl acetamide N-tert. butyl capramide N,N-dimethyl acetamide The unusual feature of the blends of m-phenyleneamine and 10 to 50 parts by weight of any one of the diamine containing any one or a mixture of the above foregoing liquifiers as such or mixtures thereof are disliquefiers is that when some of the blends are chilled persed until a uniform mixture is obtained, and the reat temperatures below zero they may freeze to a solid sulting mixture heated in any suitable container to 90- mass, but on attaining room temperature they liquefy 5 100 C. During the heating, the mixture is stirred and Without crystallization. Various blends were prepared the heating continued until a uniform melt is obtained. in accordance with the present invention and after cooling The time required to obtain a uniform melt may range to room temperature, the liquids were placed in a deep from 5 minutes to 3 hours. The liquid mixture is then freeze at 28 C. and kept there overnight. They were cooled to room temperature and filtered, after which it then permitted to stand until they reached room temperais ready for use as a curing agent. ture, and were examined twenty-four hours later for Blends of two or more liquefiers may be employed to presence of crystals as will be shown hereinafter. eifectuate solution of the m-phenylenediamine at the The liquid curing agents of the present invention are specified temperature and time of heating. The curing particularly adaptable for the curing of epoxy ether results obtained by such a mixture of liquefiers when resins characterized by the following general formula: blended with m-phenylenediamine in the aforestated prowherein R represents the divalent hydrocarbon radical portions are approximately the same as those obtained of the dihydric phenol and n represents the extent of cowith a single liquefier blended with m-phenylenediamine. polymerization. The epoxy ether resins haxe an epoxide For example, we have found that mixtures consisting of equivalent which ranges from 140 to 290. By the term 2 to 60parts by weight of N-methyl-Z-pyrrolidone and epoxide equivalent, as employed herein and in the 40 to 98 parts by weight of any one of the N-alkylappended claims is meant the grams of resin containing and N,N dialkyl-formamides and acetamides yield liqueone gram equivalent of epoxide. fying mediums for the rn-phenylenediamine and that the The liquid epoxy ethers are obtained by the procedures resulting blends are equal to the blends obtainable by described in United States Patents 2,500,600; 2,633,458; the use of the single liquefiers. 2,642,412; 2,324,483; 2,444,333; 2,520,145; 2,521,911 Compounds such as o-phenylenediamine may be added and 2,651,589; all of which are incorporated herein by to the various blends prepared in accordance with the reference for examples of the types of epoxy ether resins present invention in a concentration ranging from 0.05 that may be employed for curing with our liquid catalysts. to 5.0% as meltingrpoint depressors.

Of the several types of epoxy ether resins with varying Various blends of m-phenylenediamine with 2-pyrrolepoxide equivalents, we prefer to employ those having 40 idone, N-diethylacetamide, N-dimethylformamide, etc., an epoxide equivalent ranging between 140-165 and 225- were prepared by employing the aforestated temperatures. 290, preferably between 190-210 because of its low After cooling and filtration, the blends were observed melting point 8-12 C. (as determined by Durrans merfor appearance at room temperature and after freezing cury method) and ease of formulation with the liquid at -28 C. The parts employed were all by weight. catalysts. The results obtained are shown in Tables I and II.

TABLE 1- Properties of liquefied m-phenylenediamine blends m-Phenylenediamine N-Mcthyl-2-pyrrolid0ne Appearance of fresh melt at room temperatur Appearance at 28C do S0lid So1id. Solid Sol1d Solid. Final appearance after regaining room temperado. Liquid" Liquid S1. crystallized on Liquid Liquid, some ture. bottom. crystal ppn.

TABLE 2' Properties of liquefied m-phenylenediamine m-Phenylenediamine 50.0 70.0. 80.0 70.0... 80.0. 2-Pyn-nlidnm 50, n N-N-Dimethyl for amide 30. 0 20. 0 N-N-Diethy1acetamide 30.0 20.0. Appearance of fresh melt at room tempera- Liquid Liquid Liquid Liquld Liquid.

ure. Appearance at -28O Viscousiiquid Moderately viscous Moderately viscous Solid. Solid.

liquid. findulecooled Final appearance after regaining room tem- Liquid Liquid Mu hh crystallizado.... Do.

perature. tion on bottom.

In preparing the liquid curing catalyst of the present In order to determine the efiect of the liquid catalyst invention, to 90 parts by weight of m-phenylenediwhen compared with solid m-phenylenediamine upon the 5 physical properties of a cured epoxy ether resin, seven experiments were conducted, and the results obtained are shown in the following table. In experiment 1, 15 parts of solid m-phenylenediam ine were blended with 100 parts catalyst or resinous m-phenylenediamine adduct type catalyst. From the heat distortion points shown in the above tables it becomes clearly evident that the liquid catalysts of the present invention exert a slight plasticizof an epoxy ether resin having an epoxy equivalent of ing effect. 190 210 and the mixture heated between 7080 C. It is to be noted that although some of our liquid until the m-phenylenediamine was uniformly dispersed in catalysts after freezing at 28 C. and at attaining room the epoxy ether resin. In experiments 2 to 7 inclusive, temperature may contain some crystals and in some infrom approximately 15 to 20 parts of a mixture of liquid stances may revert to a partial solid state. This is not catalyst were added which was obtained by heating a detrimental from a practical point of view, since in the mixture of 70 parts of m-phenylenediamine and 30 parts manufacture of our liquid catalysts for commercial conof N-methyl-Z-pyrrolidone at approximately 100 C. for sumption, they will not be precooled to 28 C. After 1-2 hours with stirring. The liquid blend was allowed to the preparation of the blend, cooling to room temperacool to room temperature and filtered. The samples, ture and filtering, the blends can be stored in containers after incorporation of the curing catalyst at room temfor a long period of time. If solidification should occur, perature, were allowed to cure at room temthey can be readily remelted and brought back to room perature until the solid B stage was reached followed temperature prior to mixing with epoxy resins. by one-half hour in an oven at 100 C. and 3 /2 hours We claim: at 150 C. All parts given are by weight. The castings 1. A heat curable liquid composition comprising when subjected to physical tests gave the results shown a glycidyl polyether of a dihydric phenol having an in Table 3. epoxide equivalent ranging from 140 to 290, 50 to 90 parts TABLE 3 Epon resin castings Epon Resin (Epoxide Eq.

100-210 100.0 100.0 100.0 100.0 100.0 100.0 100.0 m-Phenylenediamine 15.0 15.0 12. 15.0 12.2 15.0 12.2 N-Methy1-2pyrro1idone 0.5 5.25 5.0 3.5 4.00 3.05 Ratio of m-Phenylenediamine to liquefier 70/30 70/30 75/25 75/25 80/20 80/20 Heat Distortion Temperature, O o 138 103 106 114.5 120.5 118.5 124 Shore D Hardness 88 88 88 88 88 88 88 In order to determine the appearance, impact, Izod and flexural strength of laminates obtained by coating Fiberglas cloth with Epon resin containing a 70/30 blend of m-phenylenediamine/N-methyl-2-pyrrolidone as a curing catalyst, three experiments were conducted and compared with a laminate in which the resin was cured by means of 15 parts of m-phenylenediamine to 100 paits of resin. In these experiments A" of laminates were prepared by coating each of 20 layers of Fiberglas cloth followed by lay-up in a wooden frame A" thick. The assembly was placed between glass panels, using Mylar film as separator. A S-pound weight was placed on top to insure proper thickness and remove recess resin. The assembly was permitted to cure to the B stage at room temperature for a period of 72 hours, and then post-cured for 3 /2 hours at 150 C. The resin content of the laminates was approximately 50%. The composition and test results are summarized in Table 4.

TABLE 4 Epon resin laminates From the foregoing illustrations it becomes clearly manifest that the liquid curing agents of the present invention are much easier to measure, handle and incorporate into liquid Epon resin formulations and Bpon resin compositions than the solid m-phenylenediamine All beers were cured at room temperature, to the B stage, for 48 hours, then baked 4 hours t 150 and 1 RCON wherein A represents a member selected from the group consisting of O, NH, N-vinyl and N-alkyl groups, R represents a member selected from the group consisting of hydrogen and alkyl groups, R represents a member selected from the group consisting of hydrogen, allyl and alkyl groups, and R represents an alkyl group.

2. A heat curable liquid composition comprising a glycidyl polyether of a dihydric phenol having an epoxide equivalent ranging from 140 to 290, 50 to parts of m-phenylenediamine and 10 to 50 parts of a liquefier consisting of N-methyl-Z-pyrrolidone.

3. A heat curable liquid composition comprising a glycidyl polyether of a dihydric phenol having an epoxide equivalent ranging from to 290, 50 to 90 parts of m-phenylenediamine and 10 to 50 parts of a liquefier consisting of butyrolactone.

4. A heat curable liquid composition comprising a glycidyl polyether of a dihydric phenol having an epoxide equivalent ranging from 140 to 290, 50 to 90 parts of m-phenylenediamine and 10 to 50 parts of a liquefier consisting of N,N-dimethyl formamide.

5. A heat curable liquid composition comprising a glycidyl polyether of a dihydric phenol having an epoxide equivalent ranging from 140 to 290, 50 to 90 7 parts of m-phenylenediamine and to 50 parts of a liquefier consisting of N,N-diethyl acetamide.

6. A heat curable liquid composition comprising a glycidyl polyether of a dihydric phenol having an epoxide equivalent ranging from 140 to 290, 50 to 90 parts of m-phenylenediamine and 10 to 50 parts of a mixture consisting of 2 to 60 parts of N-methyl-Z-pyrrolidone and 40 to 98 parts of a liquefier consisting of N,N-dimethyl formamide.

7. A heat curing composition comprising a liquid glycidyl polyether of a dihydric phenol having an epoxide equivalent ranging from 140 to 290 in admixture with a curing amount of a liquid catalyst comprising 50 to 90 parts of m-phenylenediamine and 10 to 50 parts of at least one liquefier compound selected from the group consisting of compounds of the following general formulae:

and

R1 RGON/ wherein A represents a member selected from the group consisting of 0, NH, N-vinyl and N-alkyl groups, R represents a member selected from the group consisting of hydrogen and alkyl groups, R represents a member selected from the group consisting of hydrogen, allyl and alkyl groups, and R represents an alkyl group.

8. A heat curing composition according to claim 7 wherein the liquid catalyst comprises 50 to 90 parts of m-phenylenediamine and 10 to 50 parts of a liquefier consisting of N-methyl-Z-pyrrolidone.

9. A heat curing composition according to claim 7 wherein the liquid catalyst comprises 50 to 90 parts of m-phenylenediamine and 10 to 50 parts of a liquefier consisting of butyrolactone.

10. A heat curing composition according to, claim 7 wherein the liquid catalyst comprises 50 to 90 parts of m-phenylenediamine and 10 to 50 parts of a liquefier consisting of N,N-dimethyl formamide.

11. A heat curing composition according to claim 7 wherein the liquid catalyst comprises 50 to 90 parts of m-phenylenediamine and 10 to 50 parts of a liquefier consisting of N,Ndiethyl acetamide.

12. A heat curing composition according to claim 7 wherein the liquid catalyst comprises 50 to 90 parts of m-phenylenediamine and 10 to 50 parts of a mixture consisting of 2 to 60 parts of N-methyl-Z-pyrrolidone and 40 to 98 parts of a liquefier consisting of N,N-dimethyl formamide.

13. A process of hardening into an infusible state a liquid glycidyl polyether of a dihydric phenol having an least one liquefier compound selected from the group consisting of compounds of the following general formulae:

HzC-CH1 and RI. RC ON wherein A represents a member selected from the group consisting of O, NH, N-vinyl and N-alkyl groups, R represents a member selected from the group consisting of hydrogen and alkyl groups, R represents a member selected from the group consisting of hydrogen, allyl and alkyl groups, and R represents an alkyl group, and curing the mixture of liquid catalyst and said liquid glycidyl polyether by the application of heat.

14. A process according to claim 13 wherein the liquid catalyst comprises 50 to 90 parts of m-phenylenediamine and 10 to 50 parts of a liquefier consisting of N-methyl- 2-pyrrolidone.

15. A process according to claim 13 wherein the liquid catalyst comprises 50 to 90 parts of m-phenylenediamine and 10 to 50 parts of a liquefier consisting of butyrolactone.

16. A process according to claim 13 wherein the liquid catalyst comprises. 50 to 90 parts of m-phenylenediamine and 10 to 50 parts of a liquefier consisting of N,N- dimethyl formamide.

17. A process according to claim 13 wherein the liquid catalyst comprises 50 to 90 parts of m-phenylenediamine and 10 to 50 parts of a liquefier consisting of N,N- diethyl acetamide.

18. A process according to claim 13 wherein the liquid catalyst comprises 50 to 90 parts of m-phcnylenediamine and 10 to 50 parts of a mixture consisting of 2 to parts of N-methyl-Z-pyrrolidone and 40 to 98 parts of a liquefier consisting of N,N-dimethyl formamide.

References Cited in the file of this patent UNITED STATES PATENTS 2,651,589 Shokal et a1. Sept. 8, 1953 FOREIGN PATENTS 630,663 Great Britain Oct. 18, 1949 

1. A HEAT CURABLE LIQUID COMPOSITION COMPRISING A GLYCIDYL POLYETHER OF A DIHYDRIC PHENOL HAVING AN EPOXIDE EQUIVALENT RANGING FROM 140 TO 290, 50 TO 90 PARTS OF M-PHENYLENEDIAMINE NAND 10 TO 50 PARTS OF AT LEAST ON E LIQUEFIER COMPOUND SELECTED FROM THE GROUP CONSISTING OF COMPOUNDS HAVING THE FOLLOWING GENERAL FORMULA: 